The relevant copolymers are characterized by having a repeating structure [A-CO] which implies that a unit A is positioned left and right in between carbonyl units. A is a unit derived from an olefinically unsaturated compound. The term "copolymer" includes terpolymers in which different units A are present. Thus, the copolymers are copolymers of carbon monoxide and one or more olefinically unsaturated compounds. Examples of suitable olefinically unsaturated compounds yielding a unit A are ethene, propene, butene, octene, styrene and acrylate esters. The copolymers mentioned above are known per se, cf. EP-A-121965 and EP-A-181014. Whilst these copolymers have attractive physical and mechanical properties such as yield stress, tensile strength, impact strength and flexural modulus, in some instances their processing properties can be further improved.
Melt processing, e.g., extrusion, of copolymers with an intrinsic viscosity, or limiting viscosity number (LVN), above about 2.0 dl/g (measured at 60.degree. C. in m-cresol) is adversely affected by a poor melt stability which is apparent from a notable increase of the viscosity of the melt vs. residence time. Since copolymers with a high LVN have better physical properties as engineering thermoplastic, this problem needs to be solved. Especially in fibre and sheet applications, melt-extrusion is a critical step, even for copolymers with a low LVN.
Copolymer compositions comprising a major amount of an alternating copolymer of carbon monoxide with one or more olefinically unsaturated compounds and a minor amount of at least one stabilizing additive are known in the art. The stabilizing additive may be an epoxy resin containing glycidyloxy groups, i.e. groups of the formula ##STR1## for example epoxy resins prepared from epichlorohydrin and 2,2-bis (4-hydroxyphenyl) propane. Whilst the addition of such compounds to the copolymers brings about an improvement of the stability of the melt, it appears that especially for melt processing operations in commerical production of moulded parts and extrusion at commercial scale of fibres and sheet, the melt stability could be improved even further. It is the object of the present invention to provide copolymer compositions having further improved melt stability.
It has now been found that a high degree of melt stability of the copolymers can be achieved by the addition thereto of a glycidyl ether which comprises primary hydroxy groups or keto groups. The melt stability obtainable by the addition of such glycidyl ethers is better than the melt stability obtainable by application of the known stabilizers, viz., epoxy resins prepared from epichlorohydrin and 2,2-bis(4-hydroxyphenyl)propane which epoxy resins contain secondary hydroxy groups.
The present finding is surprising in the light of U.S. Pat. No. 3,948,832 which patent deals with the stabilization of polymers of carbon monoxide and one or more olefinically unsaturated compounds having a lower content of carbonyl units than the alternating copolymers of the present invention. This patent teaches that the polymers with low content of carbon monoxide can be stabilized by the addition of epoxy compounds and that the preferred stabilizing epoxy compounds are those which are the least sensitive to oxidative degradation. Contrary to these results and quite unexpected, it has now been established that, when applying an alternating copolymer, glycidyl ethers which comprise primary aliphatic or primary benzylic hydroxy groups or ketonic carbonyl groups provide a higher degree of melt stability than glycidyl ethers which comprise secondary hydroxy groups or glycidyl ethers or epoxides which do not comprise other functional groups than the glycidyloxy or epoxy groups, despite the fact that primary aliphatic and benzylic hydroxy groups and ketonic carbonyl groups may be expected to be more sensitive to oxidation than secondary hydroxy groups or hydrocarbyl groups.
Some of the epoxy compounds which have been found to increase the melt stability of the alternating copolymers are novel compounds.